Neutrino Physics

1. Neutrino Physics • Part 1: Neutrino oscillation in vacuum • Introduction: neutrino mass, mixing and oscillation • Atmospheric neutrinos and accelerator neutrinos Caren Hagner Universität Hamburg

2. n Some Historical Remarks • 1930: neutrino postulated by Pauli (massless, neutral) • 1956: neutrino ve detected by Reines and Cowan • 1957: Wu discovered parity violation in weak interaction • 1958: Goldhaber experiment neutrinos are left handed anti-neutrinos right handed

3. 3 Neutrino Flavors • 1960: B. Pontecorvo and M. Schwartz proposed neutrino beam (from accelerated protons)→ discovery of vμ at AGS in Brookhaven by Ledermann, Schwartz and Steinberger • LEP measurement of Z0 decay width:→ 3 active neutrino flavors (mv < 80 GeV): Nv = 3.00±0.06 ve, vμ, vτ • 2000: vτdetected by DONUT experiment

4. Neutrinos in the Standard Model ? • No right handed neutrinos • Neutrinos are massless • Le, Lμ, Lτconserved

5. Neutrino Oscillations were observed→ Neutrinos have mass! JAPAN JAPAN CANADA SNO KamLAND Super-Kamiokande vμ→v,(s) OscillationΔm2 ≈ 2·10-3 eV2 ve→vμ,τ OscillationΔm2 ≈ 8·10-5 eV2 atmospheric neutrinosaccelerator neutrinos reactor neutrinos solar neutrinos Important experimental results in recent years

6. Neutrino Oscillations are a consequence of neutrino mass and mixing What is neutrino mixing?→ compare to quark CKM mixing

7. mass eigenstates mass eigenstates Quark and Lepton Mixing:Eigenstates of weak interaction ≠ Eigenstates of mass Neutrino - Mixing Quark - Mixing

8. Cabbibo-Kobayashi-Maskawa (CKM) Matrix • 3 mixing angles • 1 phase: ei CP-violation BELLE, BABAR,CLEO,… Quark-Mixing in precision measurement phase

9. of masses: md « ms « mb of mixing angles: s12 = λ, s23≈λ2, s13≈λ3 Hierarchy in Quark Mixing

10. Neutrino mixing! Neutrino mass and mixing 3 massive neutrinos: ν1, ν2, ν3 with masses: m1,m2,m3 Flavor-Eigenstates ve,vμ,vτ ≠ Mass-Eigenstates

11. Historical remark • 1957-58: B. Pontecorvo proposed neutrino oscillations(because only ve was known, he thought of v ↔ anti-v) • 1962 Maki, Nakagawa, Sakatadescribed the 2 flavor mixing and discussed neutrino flavor transition • 1967 full discussion of 2 flavor mixing,possibility of solar neutrino oscillations,question of sterile neutrinos by B. Pontecorvo

12. Parametrization of Neutrino Mixing • Pontecorvo-Maki-Nakagawa-Sakata (PMNS) Matrix: • 3 Mixing angles: θ12, θ23, θ13 • 1 Dirac-Phase (CP violating): δ θsol θ13, δ θatm • If neutrinos are Majorana particles: • 2 additional Majorana-Phases (CPV): α1, α2

13. v3 vτ vτ vτ vμ vτ θ23 vμ vμ vμ v2 ve ve θ12 θ12 θ12 v1 θ12: 29o - 39o ve θ13 θ13 ve Solar and reactor experiments Θ23: 34o - 58o θ13<13o, δ ? Atmospheric and accelerator Unknown (CHOOZ) Neutrino mixing angles

14. propagation determined bymass-eigenstates source createsflavor-eigenstates detector seesflavor-eigenstates v2 τ vτ v3 vμ W W μ p,n hadrons slightly different frequencies→ phase difference changes Neutrino Oscillations Mass eigenstates v2,v3with m2, m3 Flavor eigenstates vμ, vτ

15. k = 1, 2, 3 α = e, μ, τ neutrinos with negative helicity, mass mk, momentum pand energy is the amplitude for the transition vα→ vβ at time t General derivation of oscillation formula: now change to flavor base →

16. and using General derivation of oscillation formula:

17. Oscillation probability Probability to find vμ Probability to find vτ disappearance Survival probability Losz, Δm2 sin2(2θ) appearance Distance x in Losz 2 Flavor Neutrino Oscillations

18. Primary cosmic ray π π N N π K ν μ atmospheric neutrinos #(vμ) / #(ve) ≈ 2

20. Atmospheric Neutrino History • In less than two decades, atmospheric neutrinos have gone from being “anomalous” to being one of our main tools for theexploration of the lepton sector. • 1980s – 1990s: Skepticism was rampant! • “Neutrino experiments are hard!” • “Cosmic ray experiments are hard!” • “Oscillation experiments are hard!”

21. L ≈ 20 km atmosphericneutrinos:Ev in GeV range L ≈ 13000 km Oscillation of atmospheric neutrinos Oscillation probabilityvaries with zenith angle θ θ

22. Super-Kamiokande • solar neutrinos (8B ve few MeV) • atmospheric neutrinos (vμ,ve few GeV) • K2K accelerator neutrinos (vμ 1 GeV) • start ~2009: T2K off-axis super neutrino beam

24. electron event myon event Super-Kamiokande 50kt H2O 12000 PMTs

29. without oscillation oscillation (best fit) data SuperK – atmospheric neutrinos e–like events μ–like events νμ νe μ e

30. Atmospheric neutrinos:Analysis neutrino oscillation (full SK-I data set) E.Kearns Neutrino2004 Confirmed by MACRO, SOUDAN

33. Analysis of eventswith high L/E resolution

34. Oscillation dip!(?) First evidence of oscillation pattern? • oscillation • decay • decoherence “EVIDENCE FOR AN OSCILLATORY SIGNATURE IN ATMOSPHERIC NEUTRINO OSCILLATION.”Super-Kamiokande Apr 2004., Submitted to Phys.Rev.Lett., hep-ex/0404034

35. from L/E analysis

37. Super-Kamiokande: Accident 2001 Accident Nov 21, 2001:~7000 of 12000 PMT’simploded in chain reaction

38. Decay Pipe Focusing Devices m Proton Beam Target nm p,K Beam Dump • Beam composition (typical example): • dominantly vμ • contamination from vμ(≈6%), ve (≈0.7%), ve (≈0.2%) • vτ≲ 10-6 Neutrino beams few GeV few 100 GeV

39. K2K 250km

40. Super-Kamiokande I Inner detector 41.4m 1114620” PMTs Outer detector 18858” PMTs 39m Super-Kamiokande II • Removed Lead Glass detector • Installed SciBar and Electron • Catcher (Oct.2003~) The K2K experiment K2K-I Mar.1999 ~ Jul.2001 near neutrino detectors Muon range detector K2K-II Dec.2002~ Upgrade of near neutrino detectors

41. K2K accelerator experiment Super-Kfar detector50 kton Near Detector1 ton νμ, <Eν>=1.3 GeV KEK 300m 250km Goal: 1.0×1020 POT = 200 neutrino events in SK Data (06/1999 – 02/2004): 8.9·1019 POT events in “Far Detector” :expected without oscillation: Probability for no oscillation: <0.01%Neutrino oscillation confirmed with 3.9σ!

44. First hint for typical deformation of energy spectrum without oscillationbest fit oscillation